@catjudo: How much privacy do your kids have, and how do you decide about the amount you grant them?
I only have one child and, as I have stated previously, she is still pretty young. So the answer is...she has zero privacy. No, I take that back...at holidays/birthdays she is allowed to keep secrets that pertain to gifts/surprises. Any other secrets are prohibited.
For one thing, she knows that it's not okay or necessary to ever keep secrets from me. Should she ever encounter some pervert, he will not convince her that she should keep his bad acts a secret from me. Additionally, if she is being secretive of her actions, how will I know if she needs me to intervene and keep her safe? I certainly can't protect her and keep her safe forever. For now, I need to know what she is doing so that I can teach her how to think through a situation and make good/safe/moral choices as she encounters them.
How will I decide how much privacy to grant my daughter? I'm not sure it's really about privacy...she will develop increasing levels of autonomy as she demonstrates that she is ready. Consistently showing that she understands the importance of making good choices, understanding her choices and actions have consequences both for herself and potentially others around her, showing that she can and will be an independent thinker and not just a follower of whatever her friends are doing...all of these things will lead to gradually increased autonomy. When she stumbles along the way I will be able to pull the reigns back in a bit, re-assess the situation, help teach her where/how she went wrong and wait until she demonstrates an understanding before giving her a bit more freedom/autonomy again.
As I have stated before in this thread, this is what works for my family. I should state, it's not as if I know every detail of every conversation that my daughter has in her day. I don't grill her for a play by play of every second she is away from me (at school). But there are no conversations or questions that are off limits so she's not inclined to do something that she wouldn't want to have to tell me about. (Of course when she gets in trouble for something at school she's not eager to tell me, but she does.;))